Core-centered hydroxyapatite granule composed of micro-structure body

ABSTRACT

A granule form e d from a tubular body having an outer surface and an inner surface separated by a matrix, and at least one core defining an opening extending through the tubular body. The outer surface of the matrix is adapted to permit fluid flow into and out of the matrix.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/082,187,filed Mar. 28, 2016, now allowed, which is a continuation of U.S.co-assigned, International Application No. PCT/US2014/067375, filed Nov.25, 2014, which claims benefit of and priority to U.S. ProvisionalApplication No. 61/909,037 filed Nov. 26, 2013, the contents of whichare hereby incorporated by reference in their entirety.

FIELD OF THE DISCLOSED SUBJECT MATTER

The disclosed subject matter is a granule that facilitates cellmigration and proliferation and differentiation. The granule has agenerally tubular body having an outer surface and at least one innersurface defining one or more cores. A matrix is disposed between theouter surface of the granule and at least one inner surface. Pluralitiesof granules constitute bone regeneration filler. The granules may beused for orthopedic or dental and craniomaxillofacial applications.

BACKGROUND

Conventional granules used for bone regenerative filler have solidspherical bodies. One drawback of the solid spherical bodies is lowpopulation of cell attachment and proliferation as well as a higherfraction of surgical site was occupied by material than core-centeredgranule, less space for cell ultimately bone regeneration. It has beenunexpectedly found that granules having a generally tubular structurewith at least one core defined in the body facilitates cell migrationand/or proliferation rate.

SUMMARY

In accordance with one aspect of the subject matter, a granule thatfacilitates cell migration and/or proliferation is provided. The granulehas a hollow, tubular body. The tubular body is defined by an outersurface and an inner surface separated by a matrix. The matrix extendsbetween the outer and inner surfaces of the tubular body. The matrixcomposed of porous micro-structure to facilitate the absorption ofnatural bone repair-promoting factors in extracellular fluids result inenhancing bone regeneration. The tubular body further includes at leastone core which defines an opening extending throughout the tubular body.The core and porous micro-structure permits fluid flow into and out ofthe tubular body and facilitates cell migration and proliferation withinthe granule by providing large surface area than solid granule. Themicro-structure can be less than 5 micron, or about 10 micron to about50 micron. The inner core can be less than 150 micron, or about 200micron to about 500 micron. The granule can be less than 500 micron, orabout 1 mm to about 3 mm in length and about 700 micron to about 1500micron in diameter depending on application.

In one embodiment, the outer surface of the granule is porous. Theporous nature of the outer surface permits fluid flow into and out ofthe granule. The inner surface of the granule defines the outer contoursof a core. The defined core extends through the granule body definingthe generally tubular structure. The at least one core may be disposedin the center of the granule body or off-center. In some instances,multiple cores are defined in the granule body. For example, in oneembodiment, three cores defining three openings through the tubular bodyexist. The core permits cell migration into the granule.

A matrix interconnects the core and is disposed between the inner andouter surface of the granule body.

In some embodiments, the granule is loaded with beneficial agent. Thebeneficial agent for example can be a drug including antibacterial or abio-molecular agent including bone morphogenetic protein or transforminggrowth factor beta. In one embodiment, the beneficial agent is loadedinto the granule by way of biodegradable microspheres. The microspheresmay be, for example, disposed in the matrix or attached to the inner orouter surface of the tubular body. In another embodiment, the beneficialagents include an anti-inflammatory agent or a bone growth factor.

In another aspect, a process of fabricating hollow tubular granules, theprocess comprises: mixing HA powder and water until HA transforms intohollow filaments, subjecting the HA filaments to freezing, and heatingthe filaments. The mixing step includes stirring the HA until it forms apaste. The freezing step includes subjecting the filaments to liquidnitrogen. The heating step includes a first heating step and a secondheating step. The first heating step includes subjecting the filamentsto a temperature of about 600° C. for a period of time. The period oftime is about one hour. The second heating step includes subjecting thefilaments to a temperature of about 1230° C. for a period of time. Theperiod of time is about three hours.

In another aspect, the bone regenerative filler comprising: a pluralityof granules, wherein each of the plurality of granules includes a hollowtubular body having an outer surface and an inner surface separated by amatrix, and at least one core defining an opening extending through thetubular body, wherein the outer surface is adapted to permit fluid flowinto and out of the matrix. The plurality of granules permits cellmigration and proliferation and differentiation. The granules facilitatecell proliferation and differentiation over a period of time. Forexample, the bone regenerative filler can facilitate migration orproliferation of more than 2×105 cells in less than one week.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of various aspects, features, and embodiments ofthe subject matter described herein is provided with reference to theaccompanying drawings, which are briefly described below. The drawingsare illustrative and are not necessarily drawn to scale, with somecomponents and features being exaggerated for clarity. The drawingsillustrate various aspects and features of the present subject matterand may illustrate one or more embodiment(s) or example(s) of thepresent subject matter in whole or in part.

FIG. 1A to 1D are SEM images of granules in accordance with thedisclosed subject matter.

FIG. 2A to 2C shows SEM images of the outer surface and porousmicro-structure matrix of the granules shown in FIG. 1. FIG. 2C showsthe availability of drug or beneficial biologic reagent delivery bybiodegradable microspheres.

FIG. 3 shows images of the granules of FIG. 1 and granules of the priorart depicting that the granules of FIG. 1 facilitate greater cellmigration and exhibit better cell attachment than granules of the priorart.

FIG. 4 depicts a comparative MTT assay of the granules in accordancewith the disclosed subject matter and the granules of the prior artshowing that the granules of the subject application exhibit higher cellproliferation.

FIG. 5A illustrates a plurality of granules loaded with beneficialagents.

FIG. 5B illustrates an expected release kinetics of the granules of FIG.5A.

FIG. 6 shows greater new bone formation with invented granules thancurrent granules.

FIG. 7 depicts a comparative bone volume of the granules in accordancewith the disclosed subject matter and the granules of the prior artshowing that the granules of the subject application exhibit higher newbone formation.

FIG. 8 illustrates various applications of the bone regenerative fillerin accordance with the disclosed subject matter.

FIG. 9 is a schematic diagram of an exemplary method of making thegranule in accordance with the disclosed subject matter.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Core-Centered and PorousCeramic Granule

In one embodiment, macro—(150-500 um) and micro—(5-50 um) structuralporous ceramic granules loaded with a beneficial agent are provided. Thegranule can provide a drug delivery system by using biodegradablepolymeric spheres. For example, the granule may be suitable for boneregeneration after damage caused by injury or disease.

As depicted in FIGS. 1A to 1D, a granule 10 having a core-centeredstructure is depicted. Referring to FIG. 1B, the granule 10 has an outersurface 100, and inner surface 120 and a matrix 300 defined between theinner 120 and outer 100 surfaces. A core 200 is disposed in the granulebody and the outer contour of the core 200 is defined by the innersurface 120 of the granule. In one embodiment, as shown in FIGS. 1C and1D, the granule includes more than one inner surface 130, 140, and 150defining multiple cores 210, 220, 230.

The core-centered structure provides a larger surface area forfacilitation of cell attachment. The micro-structure 310 in the bodyshown in FIG. 2B and micro pores 110 on its outer surface shown in FIG.2A promote fluid flow, such as nutrients and/or natural bonerepair-promoting factors but not limited, in and out of the granule.Localized beneficial agents, such as drug or growth factors, can beloaded within the granule. Thus, as shown in FIG. 2C, the granule canprovide a delivery system using, for example, biodegradable polymericmicrospheres 400 loaded with beneficial agent. Various beneficial agentscan be used such as anti-inflammatory agents and bone growth factors butnot limited.

In another aspect, a method of making the granules is provided. As shownin FIG. 7, one exemplary method for making the granules includes using awater based ceramic slurry coating on fiber filament (thread, twine,yarn, etc.) followed by a freeze-dry method. The ceramic slurry wasprepared using hydroxyapatite/solution at a ratio of 0.6-0.7. Binders(3% high molecular weight polyvinyl alcohol, 3% carboxymethylcellulose,and 5% ammonium polyacrylate dispersant) were added to the slurrymixture to improve sintering and the stability of the core-centeredgranule structure. The filament was coated by prepared HA slurry, thenfrozen in liquid nitrogen. After complete freeze, it was coated againwith HA slurry to freeze in the liquid nitrogen. These steps wererepeated until the granule wall attained the desired thickness. Thegranules were lyophilized using a freeze-dryer overnight. During thelyophilization, the frozen water molecules sublimated and createdmicro-structures in the body of the granule. Heating followed at 1230°C. for 5 hours by increasing the temperature at a rate of 5° C./min.Then, the furnace was cooled permitting the sintered granules inside tocome back down to room temperature at a cooling rate of 5° C./min.During the heat treatment, the filament material dissipated leaving anopen core in the granule.

Polymeric Microspheres for Beneficial Agent Delivery

In some embodiments, the granule is loaded with beneficial agent. Forexample, the beneficial agent can be loaded in microspheres forattachment to the granule body. The non-porous or porous polymericmicrospheres for beneficial agent delivery can be fabricated usingwater/oil (double emersion) or water/oil/water (triple emersion)methods. The polymeric microspheres can be immobilized onto the granulesurface and/or inside the micro-structure using electro statictechniques. The biodegradable polymeric microspheres can be used asdelivery system for antibiotics and/or protein and/or growth factor,etc. After loading the beneficial agent, e.g., the antibiotics and/orprotein and/or growth factor, the polymeric microspheres will beattached onto the granules by surface modification by oxygen plasmatreatment and/or positive or negative coating method. In this case,after implantation of the granules into a subject, the beneficial agent,e.g., antibiotics, will be released during a first time period e.g., inone week to prevent severe infection of the surgical site. In the secondstage protein and/or growth factor or other beneficial agents will begradually released for up to four weeks to accelerate bone regeneration(FIG. 5B).

For example but without limitation, the granules can be made byhydroxyapatite (HA), tri-calcium phosphate (TCP), HA/TCP composite, anyother calcium phosphate family, bio glass, alumina, zirconia, andtitanium dioxide, etc. The polymeric microspheres can be made byPolyglycolide (PGA), Poly-L-lactide (PLLA), poly(lactic-co-glycolicacid) (PLGA), Poly-8-caprolactone (PCL), Poly-D, L-lactide (PDLLA),Poly-1,4-dioxane-2-one (PDO), Polytrimethylenecarbonate (PTMC), andPoly-13-hydroxybutyrate (PHB), etc.

The granules can be used directly as a bone substitute without abeneficial agent delivery system. However, the combined system withpolymeric microspheres may be useful for bone tumor treatment orperiodontal disease treatment.

Cellular Responses for Hollow and Porous HA Granules

Proliferation rate was higher on invented granules than current granulesduring the observed period of time. Cell attachment was clearlyevidenced for both types of granule. However, the invented granule has ahollow structure in the granule body, enhancing cell migration. Based onthese findings, the granules disclosed herein can be employed fortreatment of bony defects caused either by trauma or massive diseasesurgeries.

In addition the disclosed subject matter is also directed to otherembodiments having any other possible combination of the dependentfeatures claimed below and those disclosed above. As such, theparticular features presented in the dependent claims and disclosedabove can be combined with each other in other manners within the scopeof the disclosed subject matter such that the disclosed subject mattershould be recognized as also specifically directed to other embodimentshaving any other possible combinations. Thus, the foregoing descriptionof specific embodiments of the disclosed subject matter has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosed subject matter tothose embodiments disclosed.

What is claimed is:
 1. A process for fabricating hollow tubulargranules, the process comprising: mixing hydroxyapatite (HA) powder andwater into a slurry, applying the slurry to a filament to form hollow HAfilaments, subjecting the HA filaments to freezing, and heating thefilaments.
 2. The process of claim 1, wherein the freezing step includessubjecting the filaments to liquid nitrogen.
 3. The process of claim 1,wherein the heating step includes a first heating step and a secondheating step.
 4. The process of claim 3, wherein the first heating stepincludes subjecting the filaments to a temperature of about 600° C. fora period of time.
 5. The process of claim 4, wherein the period of timeis about one hour.
 6. The process of claim 3, wherein the second heatingstep includes subjecting the filaments to a temperature of about 1230°C. for a period of time.
 7. The process of claim 6, wherein the periodof time is about three hours.